<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
</head>

<body>
    <ul>
        <li>xxx</li>
        <li>xxx</li>
        <li>xxx</li>
    </ul>

    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
    <script>
        // 在ul后面再添加一条数据
        $('ul').append('<li>我是新来的</li>');
    </script>
</body>

</html>